The short answer is yes. The debug agent needs to deal with
JVMTI_EVENT_VIRTUAL_THREAD_START/END events for every virtual thread.
What makes it worse is when there are a large number of virtual threads
that are currently alive. They are tracked on a list of ThreadNodes that
starts to slow down debug agent performance when it gets too long. I
have a work in progress that proactively purges these ThreadNodes so the
list does not get too big. I've been meaning to revive this project for
quite some time. If you have a test case I'd be willing to experiment
with these changes some more. I could not access to the IDEA-365900 link
you provided.
Note I think after the work is done to purge ThreadNodes proactively it
might not be that hard of step to move to not needing
JVMTI_EVENT_VIRTUAL_THREAD_START/END events enabled, which will help
performance a lot more.
Chris
On 4/1/25 10:14 AM, Egor Ushakov wrote:
Hi everyone!
Is it expected that with the debugger attached creating virtual
threads is much slower?
We're getting bugs like: https://youtrack.jetbrains.com/issue/IDEA-365900
And I can reproduce it easily with jdb...
Just attaching the debugger immediately slows down virtual threads
creation significantly.
>java
-agentlib:jdwp=transport=dt_shmem,server=y,suspend=n,address=8000 app
...
6808805 (1.2046688E7 threads per second)
...
after >jdb -attach 8000
...
30215 (95986.055 threads per second)
...
Thanks,
Egor
